The present invention relates to a stationary support device for the endless, revolving dewatering wire in the forming section or wire section of a machine for the manufacture of fiber webs of paper, board, pulp, or the like. Such stationary support devices are known from U.S. Pat. No. 3,647,620 over which the invention is an improvement. Similar devices are known from U.S. Pat. Nos. 3,140,225, 3,201,308 and 3,520,775. Note also U.S. Pat. Nos. 4,865,692 and 5,129,992. Stationary support devices of this type support the endless revolving screen, called a wire, on which the fiber web is initially formed from the fiber suspension which continuously flows onto the wire.
The wire slides over the front section of a cover strip located on top of a support. The front section usually has a scraper like front edge. The front section, and particularly its front edge, leads away from the wire water which has flowed through the openings in the wire out of the fiber web which is being formed and which water is then adhering to the bottom of the wire.
The cover strip has a dewatering surface which adjoins and follows the front section in the path of the movement of the wire and which diverges from the direction of travel of the wire at an angle of inclination. This produces a vacuum below the bottom of the revolving wire which improves the removal of the water from the web. The intensity of the water removal depends on the size of the angle of inclination of the dewatering surface relative to the travel direction of the wire.
In paper making machines in which operating conditions change frequently, for instance, upon changes of the type of paper, operating speed, or the like, it is frequently necessary to change the angle of inclination of the cover strip on the stationary support device. Attempts have for a long time been made to find a reliable construction for changing the angle of inclination.
U.S. Pat. No. 4,865,692 suggests making the angle of inclination, and therefore the angle between the dewatering surface and the direction of travel of the wire, reproducible with a high degree of accuracy. Furthermore, it has been attempted to make the stationary support device as free of vibration as possible. In order to achieve these goals, the joint between the cover strip and the support device in that patent is developed as a spring plate. Furthermore, the clamping element, which is developed as an expandable tube, acts such that the device is free of play. On the one hand, the joint is under tensile stress while, on the other hand, the support elements and the corresponding oblique surfaces are held continuously in mutual contact with each other. The oblique surface is formed by a wedge bar which transmits only compressive forces.
One disadvantage of that construction is that a joint which is developed as a spring plate does not form a definite joint axis. Accordingly, upon a change in the angle of inclination, the movement of the cover strip cannot be determined in advance with sufficient accuracy. Another disadvantage is that the moveable support strip and the rigid support are developed as two C-shaped supports which engage in each other. Thus, heavy parts of complicated shape are necessary, causing a relatively high cost of manufacture and a relatively large structural height.
In contrast, the construction known from U.S. Pat. No. 3,647,620 has simpler parts and a lower height. However, in that case also, the joint is developed as a spring plate, with the above indicated disadvantages. Furthermore, the bar which serves to position the cover strip i.e., for changing the angle of inclination, which is displaceable in lengthwise direction, is made of relatively thin flat material and has obliquely extending slots for the formation of the oblique surfaces. The support elements which cooperate with the oblique surfaces are developed as pins which extend through those slots. In this case, a certain amount of play is unavoidable between the pins and the cooperating oblique surfaces. Therefore, this known construction tends to vibrate. Furthermore, the angle of inclination of the dewatering surface cannot be established with the required high precision and reproducibility.
In this respect, relatively good results, with relatively low height, can be obtained with the arrangement in U.S. Pat. No. 5,129,992. However, that still has the disadvantage that, in order to make the joint and the pair of stop surfaces free of play, a relatively large number of parts are necessary within the device, and mounting those parts is expensive.